Relating Retinotopic and Object-Selective Responses in Human Lateral Occipital Cortex

• Published in: Journal of neurophysiology Vol. 100; no. 1; pp. 249 - 267
• Main Authors: Sayres, Rory, Grill-Spector, Kalanit
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.07.2008; American Physiological Society
• Subjects: Adult; Analysis of Variance; Brain Mapping; Dominance, Ocular; Female; Humans; Image Processing, Computer-Assisted - methods; Magnetic Resonance Imaging - methods; Male; Occipital Lobe - blood supply; Occipital Lobe - physiology; Oxygen - blood; Pattern Recognition, Visual - physiology; Photic Stimulation - methods; Reaction Time - physiology; Retina - physiology; Visual Fields - physiology; Visual Pathways - blood supply; Visual Pathways - physiology
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.01383.2007

1 Neurosciences Institute and 2 Department of Psychology, Stanford University, Stanford, California Submitted 21 December 2007; accepted in final form 2 May 2008 What is the relationship between retinotopy and object selectivity in human lateral occipital (LO) cortex? We used functional magnetic resonance imaging (fMRI) to examine sensitivity to retinal position and category in LO, an object-selective region positioned posterior to MT along the lateral cortical surface. Six subjects participated in phase-encoded retinotopic mapping experiments as well as block-design experiments in which objects from six different categories were presented at six distinct positions in the visual field. We found substantial position modulation in LO using standard nonobject retinotopic mapping stimuli; this modulation extended beyond the boundaries of visual field maps LO-1 and LO-2. Further, LO showed a pronounced lower visual field bias: more LO voxels represented the lower contralateral visual field, and the mean LO response was higher to objects presented below fixation than above fixation. However, eccentricity effects produced by retinotopic mapping stimuli and objects differed. Whereas LO voxels preferred a range of eccentricities lying mostly outside the fovea in the retinotopic mapping experiment, LO responses were strongest to foveally presented objects. Finally, we found a stronger effect of position than category on both the mean LO response, as well as the distributed response across voxels. Overall these results demonstrate that retinal position exhibits strong effects on neural response in LO and indicates that these position effects may be explained by retinotopic organization. Address for reprint requests and other correspondence: R. Sayres, Psychology Dept., Stanford University, Stanford, CA 94305 (E-mail: sayres{at}psych.stanford.edu )